STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 53 



genus, while in the next layer the forms are stunted. Both firs and 

 pines are wanting in the upper portion of the mass. Sernander and 

 Kjellmark°° discovered that in northern Nericke, Sweden, the succes- 

 sion is (i) Living peat; (2) sphagnum-peat; (3) bed of stumps and 

 roots; (4) sphagnum-peat, passing downward into peat composed 

 chiefly of Phragniitcs and Eqnisctnm. The stump layer has birches 

 with needles and bark of Picea ahies, Finns sylz'estris with fruits, 

 seeds and leaves of other plants. 



In the Harz locality, increasing wetness destroyed the trees ; in 

 Nericke, trees advanced when the moisture decreased, only to be 

 destroyed when once more the moisture increased. 



According to Poole,"^ the great turbary, known as the South 

 Marsh, is double. The upper part is 7 to 8 feet thick and is worked 

 for use as fuel ; the lower portion, of about the same thickness, has 

 on its surface everywhere the stumps and roots of trees, standing 

 as they grew. Woodward states that the peat is composed mostly of 

 sedges, so that it is clear that tlie restoration of marsh conditions led 

 to destruction of the forest which had grown on the bog surface. 

 Skertchly^- recognized five successive forests in the peat of Wood 

 fen near Ely. Number i, at the bottom, is of oak and the trees are 

 rooted in the Kimmeridge Clay ; Number 2 is at an average distance 

 of 2 feet above the other and consists of yews and oaks, the lower 

 forest having perished before this began, as roots of Number 2 some- 

 times rest on stumps of Number i ; at 3 feet higher, are the remains 

 of another forest, all firs, and another is just above that; while im- 

 mediately below the present surface is still another, resembling the 

 modern trees of the region. There were five successive forests, of 

 which all except the first were rooted in the peat. As Skertchly re- 

 marks, it is evident that, while in general the climate of the Fenland 

 may have favored peat making, still there were intervals when peat 

 was formed, if at all, in very limited areas, the other portions being 



5° R. Sernander und K. Kjellmark, " Eine Torfmooruntersuchung aus 

 dem nordlichen Nericke," Bull. Gcol. Inst. Upsala, Vol. II., 1896, pp. 321, 324. 



51 G. S. Poole, cited by H. B. Woodward, in " Geology of Eastern Som- 

 erset," Mem. Geol. Surv. London, 1876, pp. 146, 156. 



^- S. B. J. Skertchly, "The Geology of the Fenland," pp. 130, 151, 165, 

 168, 169. 



